Pre-implantation Genetic Diagnosis (PGD) stands as a groundbreaking reproductive technology, offering prospective parents the opportunity to mitigate the risk of passing on inherited genetic conditions to their offspring. While not typically necessary for couples facing infertility, PGD becomes a vital consideration when there’s a known family history of a specific genetic disorder. Furthermore, advancements in genetic screening may reveal that couples undergoing in vitro fertilization (IVF) are also at risk of transmitting inherited conditions, making PGD a relevant and powerful option for them as well.
PGD’s versatility extends to virtually any inherited condition where the precise genetic mutation has been identified. However, it’s crucial to understand that the process necessitates the development of a bespoke genetic test tailored to each couple’s unique genetic profile. This personalized test design phase can take several months to complete before an IVF cycle can even commence.
The PGD procedure is intricately linked with IVF. It begins with stimulating the ovaries to mature and retrieve multiple eggs. These oocytes, or immature egg cells, are then fertilized with a single sperm through a technique called intracytoplasmic sperm injection (ICSI). ICSI ensures fertilization by directly injecting a sperm into each egg.
The resulting embryos are carefully nurtured in a laboratory setting until they reach the six-to-eight-cell stage, typically around day three of their development. At this juncture, a delicate embryo biopsy is performed. This involves the removal of one to two cells from each embryo. Importantly, this biopsy procedure is meticulously carried out to avoid any harm to the remaining cells within the embryo, ensuring its continued viability.
These extracted cells are then subjected to rigorous analysis to detect the presence of specific genetic conditions. Embryos identified as being free from the targeted genetic condition are then selected for transfer back into the woman’s uterus, usually around day five of embryo development. This selective transfer significantly increases the likelihood of a healthy pregnancy and birth.
Two primary techniques are employed for the genetic evaluation of the biopsied cells:
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Polymerase Chain Reaction (PCR): PCR is a molecular biology technique used to amplify specific DNA sequences. In the context of PGD, PCR creates multiple copies of the gene of interest. This amplification is crucial as it allows for the detection of even minute amounts of DNA, enabling accurate diagnosis of genetic conditions from just a few cells.
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Fluorescent In Situ Hybridization (FISH): FISH is a cytogenetic technique that allows laboratory specialists to count the number of chromosomes within an isolated cell. FISH is primarily utilized to identify abnormalities in chromosome number, such as in cases of Down syndrome, or to detect chromosomal translocations, which are structural defects within chromosomes.
For couples considering PGD, choosing a facility with proven expertise in both embryology and genetics is paramount. A skilled embryology laboratory team with extensive experience in embryo micromanipulation and biopsy is essential for maximizing the success and safety of the procedure. Furthermore, access to experienced genetic counselors who can seamlessly coordinate the PGD cycle with the IVF team and the genetic testing laboratory ensures a streamlined and supportive patient experience.
